'perpendicularity' originates from Latin via Medieval Latin and Late Latin word components: 'perpendiculum' (a plumb line) and the adjective-forming element that became 'perpendicular', plus the noun suffix '-ity' from Latin '-itas'. 'per-' meant 'thoroughly' and 'pendere' meant 'to hang'.

'perpendicularity' developed from Medieval Latin 'perpendicularis' (meaning 'vertical, hanging down'), which passed into Middle French as 'perpendiculaire' and later into English as 'perpendicular'; the abstract noun 'perpendicularity' was formed in Modern English by adding the suffix '-ity'.

Initially, related words referred specifically to a plumb line or vertical hanging (the sense of 'hung down' or 'vertical'); over time the meaning broadened to the general geometric/engineering sense of 'being at right angles' and the abstract quality of that condition.